The present invention relates to an input torque detecting device for power steering, more particularly, an input torque detecting device which converts a relative rotation of an input shaft and an output shaft into a movement in the direction of a shaft so as to detect torque.
Heretofore, as an input torque detecting device for power steering, for example, a device for detecting input torque by converting the relative rotation of an input shaft and an output shaft resulting from torsion of a torsion bar based on input torque into an amount of slide in the direction of a shaft and detecting the amount of slide as proposed in Japanese Patent Application No. Hei 7-182151 is well known. The input torque detecting device of Japanese Patent Application No. Hei 7-182151 will subsequently be described with reference to FIGS. 6 through 9.
As shown in FIG. 6, an input shaft 101 in which torque is input from a steering wheel is rotatably held in a gear box 118 through a bearing 121 and also connected to an output shaft 103 through a torsion bar 102 which is connected to the inside of the input shaft 101. The output shaft 103 is rotatably held in the gear box 118 through a bearing 122 and also engaged with a rack shaft 105 through a pinion gear 104, whereby input torque is applied to a steered side through the rack shaft 105.
A cylindrical sleeve 107 is installed at a common outer circumference of the input shaft 101 and the output shaft 103. As shown in FIG. 7, at an inner circumference of the sleeve 107, a pair of pins 108 are installed as members for engaging with the input shaft 101 at an interval of 180 degrees and also a pair of shaft line direction holes 109 which extend in the direction of a shaft line are formed as members for engaging with the output shaft 103 at an interval of 180 degrees. Incidentally, the pins 108 and the shaft line direction holes 109 are installed in such a manner that they get out of position to each other by 90 degrees.
On the other hand, as shown in FIGS. 8 and 9, two spiral grooves 113 which extend in a direction diagonal to a shaft line are formed at an outer circumference of the input shaft 101 as sections for engaging with the pins 108. Further, pins 114 are formed at the output shaft 103 as members for engaging with the shaft line direction holes 109.
Further, an annular detection groove 115 is formed at an outer circumference of the sleeve 107 and a detection lever 116 of a sensor 117 (for example, a potentiometer) is engaged with the detection groove 115.
Due to such constitution, in a conventional input torque detecting device, the input shaft 101 and the output shaft 103 make relative rotations as a result of torsion of a torsion bar which is caused by inputting input torque from a steering wheel in the input shaft 101. At this time, in a relation to the output shaft 103, the sleeve 107 is allowed to make a relative movement only in a direction along the shaft line direction holes 109 and is prohibited from making a relative rotation. On the other hand, in a relation to the input shaft 101, the sleeve 107 makes relative rotations sliding in the direction of a shaft in spiral orbit along the spiral grooves 113. Thus, an amount of torsion of the torsion bar 102 is converted into an amount of slide of the sleeve 107, and the amount of slide is detected by the sensor 117 as an amount of operating the detection lever 116 which is engaged with the sleeve 107. More specifically, input torque is detected by the sensor 117, and an electric motor or the like which is not shown in the drawings generates auxiliary torque according to the magnitude and direction of the input torque detected.
However, the conventional input torque detecting device is accompanied with the following problems.
First, the conventional input torque detecting device requires that the pins 108 are fitted to the sleeve 107 and the pins 114 to the output shaft 103, respectively, as engaging members, whereby a large number of parts are used. Further, it requires a process which pin holes for fixing pins are machined in the sleeve 107 and the output shaft 103 and then the pins 108 and 114 are pressed into the pin holes. Surplus manufacturing costs are entailed and man-hours for assembly increase.
Second, due to line contact of the spiral grooves 113 with the cylindrical pins 108 and the shaft line direction holes 109 with the cylindrical pins 114, operation of the device easily causes abrasion of these pins 108 and 114.
Third, since the spiral grooves 113 formed at the input shaft 103 are square, plastic working cannot be carried out and machining is required, whereby manufacturing costs become higher.
In this regard, Japanese Patent Application No. Hei 7-182151 discloses an embodiment in which a ball rotatably held at the sleeve 107 is used as an engaging member, but it does not lead to the fundamental solution of the problems described above. Further, in order to prevent the ball from falling from the sleeve 107, a ball hole must be bored in the sleeve 107, whereby manufacturing costs are increased again.
The present invention is made in consideration of such problems. An object of the present invention is to provide an input torque detecting device for power steering which is capable of reducing parts in number, facilitating assembly, and decreasing manufacturing costs.
According to the present invention, in an input torque detecting device comprising an input shaft in which torque is input from a steering wheel side, an output shaft being linked to a steered side, a torsion bar to be equipped between the said input shaft and output shaft, a movable body which is slidably arranged at the said input shaft and output shaft in the direction of a shaft, converting means for converting a relative rotation of the said input shaft and output shaft into a slide of the movable body in the direction of a shaft, and detecting means for detecting an amount of slide of the movable bodies, a cylindrical sleeve to be arranged as the said movable body at a common outer circumference of the said input shaft and output shaft is equipped and also a diameter expansion section is installed at any one of the outer circumferences of the said input shaft and output shaft. Further, the said converting means have a plurality of splines which are formed extending in a direction diagonally to a shaft line at the said diameter expansion section and an inner circumference of the said sleeve, respectively, and engagement means which engage either of the input shaft or the output shaft with the said sleeve in such a manner that only a slide in the direction of a shaft is allowed. At least one end of the said splines is opened, an undulation section is installed orthogonally to a shaft center at an outer circumference of the said sleeve, and a detection lever of the detecting means is engaged with the undulation section. Thus, when a relative rotation between the input shaft and the output shaft arises resulting from torsion of the torsion bar based on input torque, in a relation to the input shaft or the output shaft, the sleeve makes relative rotations along a spiral orbit which is determined by a plurality of splines formed extending in a diagonal direction and also makes a relative movement in the direction of a shaft. Input torque is detected by detecting an amount of slide of the sleeve in the direction of a shaft by the detecting means. When auxiliary torque arises based on the magnitude and direction of the input torque, an appropriate power assist can be achieved. In this case, a section engaging the sleeve with the input shaft or the output shaft is composed of a plurality of splines. These splines can be formed in one united body with the sleeve and either the input shaft or the output shaft. Thus any other engaging member of a different kind is not required, whereby the number of parts and the man-hours for assembly in manufacturing can be decreased and costs can be reduced. Further, since spline connection is applied to the sleeve and either the input shaft or the output shaft by a plurality of splines, a contact area of the engaging section can be increased. This leads to a decrease in contact pressure. As a result, abrasion of the engaging section can be reduced, and durability and reliability of the input torque detecting device can be improved. Further, as the plurality of splines can easily be processed, time and labor for machining can be curtailed, and manufacturing costs can be decreased. Also, the undulation section which is a section of engaging the sleeve with the detection lever can easily be processed, whereby manufacturing costs can be decreased. Further, a distance between the detecting means and the sleeve can be shortened by adjusting the size of the diameter expansion section. Therefore, length of the detection lever can be shortened, detection accuracy of the detecting means can be improved, and operation of the sleeve can be improved.
Further, according to the present invention, means for engaging the sleeve with either of the said input shaft and output shaft is a pair of splines which are formed at an outer circumference of either the input shaft or the output shaft and at an inner circumference of the sleeve, respectively, at an interval of 180 degrees extending in the direction of a shaft line. Due to this arrangement, the linear splines can be formed in one united body with the sleeve and either the input shaft or the output shaft. Thus, the number of parts and the man-hours for assembly can be reduced, the pair of splines extending in the direction of a shaft line can easily be processed, and the manufacturing costs can be decreased. Also, due to spline connection by means of the pair of splines extending in the direction of a shaft line, a contact area of the engaging section can be increased, abrasion of the engaging section can be reduced, and durability of the device improves.
Further, according to the present invention, a plurality of slanting splines to be formed at either the input shaft or the output shaft are formed at the diameter expansion section which is installed at an outer circumference of either the input shaft or the output shaft, and at least one end of these splines is opened. Thus, the plurality of slanting splines can easily be processed.
Further, according to the present invention, a pair of splines facing in the direction of a shaft line to be formed at either the input shaft or the output shaft are formed at a diameter expansion section which is installed at an outer circumference of either the input shaft or the output shaft, and at least one end of these splines is opened. Thus, the pair of splines facing in the direction of a shaft line can easily be processed.